bitops: find first set bit

Provide toolchain abstraction for __builtin_ffs{,l,ll} gcc built-in
intrinsics.
Add associated unit tests.

Signed-off-by: Tyler Retzlaff <[email protected]>
Signed-off-by: Andre Muezerie <[email protected]>

app/test/test_bitcount.c

@@ -112,6 +112,42 @@ test_popcount64(void)
 	return 0;
 }
 
+static int
+test_bit_scan_forward(void)
+{
+	unsigned int bit_nr;
+
+	TEST_ASSERT((bit_nr = rte_ffs32(0)) == 0,
+		"rte_ffs32 returned unexpected %d", bit_nr);
+
+	for (int i = 0; i < 32; ++i) {
+		uint32_t n = RTE_BIT32(i);
+
+		TEST_ASSERT((bit_nr = rte_ffs32(n)) == (unsigned int)(i+1),
+			"rte_ffs32 returned unexpected %d", bit_nr);
+	}
+
+	return TEST_SUCCESS;
+}
+
+static int
+test_bit_scan_forward64(void)
+{
+	unsigned int bit_nr;
+
+	TEST_ASSERT((bit_nr = rte_ffs64(0)) == 0,
+		"rte_ffs64 returned unexpected %d", bit_nr);
+
+	for (int i = 0; i < 64; ++i) {
+		uint64_t n = RTE_BIT64(i);
+
+		TEST_ASSERT((bit_nr = rte_ffs64(n)) == (unsigned int)(i+1),
+			"rte_ffs64 returned unexpected %d", bit_nr);
+	}
+
+	return TEST_SUCCESS;
+}
+
 static struct unit_test_suite bitcount_test_suite = {
 	.suite_name = "bitcount autotest",
 	.setup = NULL,
@@ -123,6 +159,8 @@ static struct unit_test_suite bitcount_test_suite = {
 		TEST_CASE(test_ctz64),
 		TEST_CASE(test_popcount32),
 		TEST_CASE(test_popcount64),
+		TEST_CASE(test_bit_scan_forward),
+		TEST_CASE(test_bit_scan_forward64),
 		TEST_CASES_END()
 	}
 };

lib/eal/include/rte_bitops.h

@@ -958,6 +958,54 @@ rte_popcount64(uint64_t v)
 	return (unsigned int)__popcnt64(v);
 }
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Search v from least significant bit (LSB) to the most
+ * significant bit (MSB) for a set bit (1).
+ *
+ * @param v
+ *   The value.
+ * @return
+ *   Bit index + 1 if a set bit is found, zero otherwise.
+ */
+__rte_experimental
+static inline unsigned int
+rte_ffs32(uint32_t v)
+{
+	unsigned long rv;
+
+	if (_BitScanForward(&rv, v) == 0)
+		return 0;
+
+	return (unsigned int)rv + 1;
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Search v from least significant bit (LSB) to the most
+ * significant bit (MSB) for a set bit (1).
+ *
+ * @param v
+ *   The value.
+ * @return
+ *   Bit index + 1 if a set bit is found, zero otherwise.
+ */
+__rte_experimental
+static inline unsigned int
+rte_ffs64(uint64_t v)
+{
+	unsigned long rv;
+
+	if (_BitScanForward64(&rv, v) == 0)
+		return 0;
+
+	return (unsigned int)rv + 1;
+}
+
 #else
 
 /**
@@ -1044,6 +1092,44 @@ rte_popcount64(uint64_t v)
 	return (unsigned int)__builtin_popcountll(v);
 }
 
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Search v from least significant bit (LSB) to the most
+ * significant bit (MSB) for a set bit (1).
+ *
+ * @param v
+ *   The value.
+ * @return
+ *   Bit index + 1 if a set bit is found, zero otherwise.
+ */
+__rte_experimental
+static inline unsigned int
+rte_ffs32(uint32_t v)
+{
+	return (unsigned int)__builtin_ffs(v);
+}
+
+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Search v from least significant bit (LSB) to the most
+ * significant bit (MSB) for a set bit (1).
+ *
+ * @param v
+ *   The value.
+ * @return
+ *   Bit index + 1 if a set bit is found, zero otherwise.
+ */
+__rte_experimental
+static inline unsigned int
+rte_ffs64(uint64_t v)
+{
+	return (unsigned int)__builtin_ffsll(v);
+}
+
 #endif
 
 /**